Bee Diseases and their Control
This leaflet describes important symptoms, the transmission and control of the three major brood diseases
and the one important adult disease of honey bees.
The figures and portions of the text are taken from
material prepared by the United States Department of
Agriculture.
Diseases of the brooD
Foulbrood, European Foulbrood and Sacbrood.
american foulbrood
Cause: Bacillus larvae, a microscopic spore-forming
bacteria.
effect: American foulbrood (AFB) is the most widespread and the most destructive of the brood diseases. At first, the strength of an infected colony is
not noticeably decreased and only a few dead larvae or
pupae may be present. The disease may not develop to
the critical stage when it seriously weakens and finally
kills the colony until the following year, or it may advance rapidly and seriously weaken or kill the colony
the first season.
Symptoms: Death of an infected larva usually takes
place after the cell has been sealed and the cocoon
has been spun. First the capping of the diseased cell
becomes moist and darkens in color. Then as the larva
shrinks, the capping is drawn into the mouth of the cell
so the convex capping becomes concave. Worker bees
may puncture this sunken capping and may eventually remove it altogether. At death, the diseased larva
changes from a normal pearly white color to a creamy
brown, then gradually darkens. These larval remains
can be drawn out into a brown thread or rope. As the
larva dries up, it becomes dark brown. The final state
is a very dark brown, rather rough scale that lies
uniformly on the lower side of the cell and extends
from just below the mouth of the cell down to the base.
These scales stick very tightly to the cell and can be
removed only with great difficulty. If death oc- curs at
the pupal stage, the tongue of the pupa (false tongue)
protrudes from the scale across the cell. The odor of
dead brood is very characteristic and has been
described as resembling a glue pot or glue color.
The overall appearance of a comb infected with American
foulbrood is patchy (pattern referred to as “shotgun”)
because of the intermixed diseased and healthy cells
and also because the remains vary from the ropy moist
MAAREC Publication 4.9
Revised November 2005
larvae in cells with dark sunken or perforated capping to
the dry scales lying in open cells whose cappings have
been chewed away completely by the bees.
transmission: The spores are fed to young larvae by
the nurse bees. They then germinate in the gut of the
larva and multiply rapidly, causing the larva to die soon
after it has been sealed in its cell. By the time of death
of the larva, the new spores have formed. When the
house bees clean out the cell containing the dead larva,
these spores are distributed throughout the hive and
more and more larvae become infected. The honey in
an infected colony becomes contaminated with spores
and can be a source of infection for any bee that gains
access to it. For example, as a colony becomes weak, it
cannot defend itself from attacks by robber bees from
strong nearby colonies; these robbers take back the
contaminated honey to their own colony and start
again the cycle of infection and robbing. The beekeeper
also may inadvertently spread the disease by exposing
contaminated honey to other bees or by interchange of
infected equipment. Using stored equipment contaminated by spores will lead to a new infection even after
years of storage. Moreover, drifting bees or swarms issuing from an infected colony may spread the disease.
Control: Sanitation and elimination of disease reservoirs is a necessity for adequate control of American
foulbrood. The traditional control measure is to kill all
bees in an affected colony and then destroy bees and
their comb by burning. The hive bodies, bottom board
and covers can be salvaged by scraping thoroughly and
then charring the inside portions and/or boiling in a
lye solution.
Ethylene oxide (ETO) combined with a drug treatment
has been found to effectively control AFB. ETO gas must
be administered under heat and pressure and only a
few states have facilities available for treatment with
ETO. Contact the Apiary Inspection Service to determine
what facilities are available in your state. Maryland and
Delaware have used an ETO chambers.
Drug treatment suppresses development of the AFB
pathogen. However, treatment does not destroy spores.
Larger beekeepers regularly feed drugs as a prophylactic. The drug oxytetracycline (Terramycin) applied as a
dust or in sugar syrup or as a grease patty is permitted in most states. No drug should be fed when there
is danger of contaminating the honey crop. Follow the
directions carefully and do not overdose. Remember
that spores may and often do survive feeding of these
drugs and colonies may break down with disease when
treatment is terminated.
Terramycin Soluble Powder is used for the prevention
of European and American foulbrood. This product is
available in a 6.4-oz packet. The package directions
can be confusing; to determine the correct application
amounts, follow these directions:
• The legal dose is 200 mg, three times, at 4–5 day
intervals.
• One package contains 10 grams (10,000 mg) of Terramycin.
• 10,000 mg ÷ 200 = 50 treatments per package.
• 50 treatments ÷ 3 = 17, so one 6.4-oz package treats
17 colonies three times each.
The package calls for one teaspoon of Terramycin
Soluble Powder per ounce of powdered sugar. Use the
following calculations:
• One level teaspoon of Terramycin = 200 mg, or one
treatment.
• Each 6.4-oz package contains 50 treatments, so mix
one package with 50 oz (just over 3 lbs) of powdered
sugar. Store in a tightly sealed container. (Exposure
to air or moisture will break down Terramycin.)
• The dosage per colony is 2 tablespoons of this mixture,
given three times, 4–5 days apart (for a total of 600
mg per colony). Spread two tablespoons of the Terramycin mixture over the end of the top bars in the
hive body with the most brood.
Preventative treatments can be applied to colonies in the
fall after honey supers are off and again in the spring
45 days before putting honey supers on.
Premixed Terramycin formulations:
Terra Brood Mix® (Mid-Con)
Tetra Bee Mix® (Dadant)
Terra Patties® (Mann Lake)
Terra Pro® (Mann Lake)
Terra Brood Mix or Tetra Bee Mix. These products are
identical. This is premixed Terramycin and is used in
the prevention of American and European Foulbrood. It
takes the guesswork out of how much Terramycin and
sugar to mix together. For both products, the dosage is
2 tablespoons, three times, 4–5 days apart. Spread the
Terramycin mixture over the end of the top bars in the
hive body with the most brood in it. Treat colonies in the
fall after honey supers are off and again in the spring at
least 45 days before putting honey supers on.
The U.S. Food and Drug Administration (FDA) has approved TYLAN (tylosin tartrate) Soluble for the control
of American foulbrood (Paenibacillus larvae) in honey
bees. This drug is used only in cases of AFB that has
been identified as resistant to Terramycin by the state
apiary inspection service.
european foulbrood
Cause: Streptococcus pluton, a microscopic lancetshaped bacteria.
effect: European foulbrood (EFB) is most common
in the spring when brood rearing is at its height,
though usually the earliest reared brood is not affected.
Sometimes the disease appears suddenly and spreads
rapidly within infected colonies; at other times it spreads
slowly and does little damage. European foulbrood may
severely weaken a colony but usually does not kill an
entire colony. As a rule, it subsides by mid-summer,
but occasionally it continues to be active during summer and fall or may reappear in the fall. A good honey
flow seems to hasten recovery.
Symptoms: Larvae diseased by European foulbrood
move restlessly within their cells and, therefore, when
they die, are usually twisted in the cells. However, some
larvae may be stretched out lengthwise from the top to
the base. the larva collapses as though it had been
melted, turns yellowish brown, and eventually dries to
form a loosely attached brown scale. The consistency of
recently dead larvae varies but it is not ropy. The odor
of the larval remains also varies but it is usually a sour
odor. the scales are loose within the cells and can be
removed readily. Combs containing larvae infected with
European foulbrood usually present a rather uniform
appearance because the cells are not usually sealed.
rearing season, but it is most common during the first
half of the season. Usually it subsides after the main
honey flow starts.
However, the beekeeper should learn to recognize
sacbrood so it will not be mistaken for the serious
foulbrood diseases.
Sacbrood may appear at any time during the broodrearing season, but it is most common during the first
half of the season. Usually it subsides after the main
honey flow starts.
Symptoms: Scattered among the healthy brood are
cells containing dead brood. Their cappings are dark
and may be punctured or partly removed by the
adult bees.
About the time the cell is sealed, the larva dies. When it
does, the head end turns up like the end of a canoe
and remains in that position; also the pearly white
color begins to darken, and the skin then becomes
tough and the contents watery. At that stage, the larva,
which resembles a liquid-filled sac, can be removed
from the cell intact; hence, the name sacbrood. The
dead larva then continues to dry and harden until the
dried-down scale is almost black. The head end is
usually the darkest. scales of larvae dead of sacbrood
can be removed from the cell easily.
transmission: The organism becomes mixed with the
brood food fed to the young larva by the nurse bees,
multiplies rapidly within the gut of the larva, and causes
death within about 4 days after egg hatch. House bees
cleaning out the dead larvae from the cells distribute
the organism throughout the hive. Since the honey of
infected colonies and the beekeepers equipment are
undoubtedly contaminated, subsequent spread of the
disease is accomplished by robber bees, exposure of
contaminated honey be the beekeeper, interchange of
contaminated equipment among colonies, and
perhaps to some extent, by drifting bees. The bacteria
is not a spore forming species.
transmission: The virus is probably fed to the young
larva by the nurse bees in the brood food. It multiplies
rapidly within the larva until it causes death. Then the
house bees cleaning out the cells probably distribute
the virus to other larvae within the hive. The disease is
usually limited to one or a few colonies in an apiary.
Control: requeening of badly infected colonies usually
will help clear up the disease. Moving colonies to areas
where there is a better honey flow or mix of flowering
plants also usually decreases disease symptoms. Feeding of the drug oxytetracycline (Terramycin) as a dust
may be necessary in severe cases. Follow directions for
feeding terramycin under AFB.
Nosema
sacbrood
Cause: A virus.
effect: Sacbrood is a widely distributed disease, but
it usually does not cause serious loss. However, the
beekeeper should learn to recognize sacbrood so it will
not be mistaken for the serious foulbrood diseases.
Sacbrood may appear at any time during the brood-
Control: No known control exists. In severe cases moving the colony or requeening may help. Colonies usually
recover from sacbrood without beekeeper aid.
Diseases of the aDuLt
Cause: Nosema apis, a small, single-celled protozoan.
effect: Nosema disease is widespread and can cause
extensive losses of adult bees. Workers with Nosema
disease have a life span shortened by 10 to 40%. There
is reduced brood production in a colony affected with
the disease. It is also responsible for supersedure of
queens especially in colonies established from infected
package bees. Colonies infected with Nosema have
heavier winter losses and there is a decrease in foraging
and colonies store less honey. The decrease in honey
production may approach 50% of production of healthy
Nosema-free colonies. Surveys of Delmarva apiaries
have shown that better than 50% of all colonies can be
expected to contain detectable levels of Nosema.
Symptoms: No symptoms are specifically indicative of
Nosema. Inability of bees to fly when they leave the
hive, excreta on combs or entrance boards, and a
pile of dead bees on the ground in front of the hive
may be manifestations of Nosema infection, but they
may also be caused by other abnormal conditions.
Also, the disease may be present without any obvious
signs. however, if crawlers or unusual numbers of dead
bees are seen in the apiary or if a colony fails to build
up properly in the spring Nosema disease should be
suspected. To definitely ascertain whether Nosema
disease is present requires microscopic examination
of the abdomens of older adult bees.
transmission: The spores of Nosema apis enter the
body of the adult bee through the mouth and germinate in the gut. After germination, the active phase of
the organism enters the digestive cells that line the
midgut of the adult bee where they multiply rapidly.
The contents of these cells are used as a food supply
until reproduction ceases and new spores are formed.
The cell then ruptures and sheds the new spores into
the midgut where they pass down through the small
intestine to the rectum. Here these accumulate and are
voided in the excreta of the bee. The cycle begins over
again when the spores contaminate the water or food
of other bees. Spores will remain viable for many
months in dried spots of excreta on brood combs.
They lose their viability within a few days in water exposed to direct sunlight, and they are also easily killed
by heat and by some fumigants.
Near the end of winter combs are often soiled with
excreta dropped by infected workers. Other bees lap
up the newly voided liquid excreta or become infected
later when they pick up the spores in the dried excreta
as they clean the soiled combs during the spring expansion of the brood nest. Thus, at this season, the
disease within the colony increases rapidly for a
time, and a colony may dwindle in the spring because
of the premature death of overwintered bees. Usually
the colony survives and the proportion of infected bees
begins to decline rapidly. This decline occurs because
the excreta are normally voided away from the hive
when regular flights become possible in later spring.
The infected bees no longer transmit the disease by
excreta to the other occupants of the hive. Since the
old bees now die off and are replaced by healthy bees
emerging from the brood combs the disease is not
detectable in the colony by the end of the season.
However, enough spores remain on the combs from the
previous winter to infect a few bees in the cluster that
forms when winter sets in again. These infected bees
then form the nucleus for a repetition of the cycle.
The disappearance of the infection during the summer seems to indicate that outside agencies such as
drinking water, flowers, or vegetation are not important in the spread of the disease. Also, the honey is
probably not contaminated to any significant degree,
since excreta are not deposited on the combs while
the cells are being filled and sealed. The spread of
Nosema disease occurs chiefly because of the use
of contaminated equipment, infected package bees,
infected queens and her attendant workers, and the
robbing of infected hives.
Control: The drug fumagillin (Fumidil-B) is approved for
Nosema control. It should be fed only in a sugar syrup
with feeding and mixing directions followed carefully.
The recommended feedings is 100 mg. fumagillin (about
1 teaspoon) to 1 gallon of sugar syrup (mix 2 parts sugar
to 1 part water). Feed two or three gallons in the fall
and a minimum of one gallon to newly installed spring
packages. Spring syrup feeding would be 1 part sugar
to 1 part water. The drug will not completely eliminate
Nosema since the disease spores can survive drug
treatment. Proper use of drug chemotherapy has been
shown to increase honey yields by as much as 30 to
50 percent.
To eliminate disease spores from bee equipment, treatment in a heated chamber (1208F for 24 hours) has
been found to be completely effective. Ethylene Oxide
(ETO) fumigation also eliminates Nosema spores when
combined with the heat treatment as will acetic acid and
heat. Treating equipment followed by treatment of bees
with fumagillin is the best method to reduce Nosema
losses and promote colony health.
CoMParatiVe sYMPtoMs of brooD Diseases
Symptoms
American foulbrood
European foulbrood
Sacbrood
Appearance of brood comb
Sealed brood.
Discolored, sunken or
punctured cappings.
Unsealed brood. Some
sealed brood in
advanced cases with
discolored, sunken or
punctured cappings.
Sealed brood.
Scattered cells with
punctured cappings,
often with two holes.
Age of dead brood
Usually older sealed
larvae or young
pupae.
Usually young unsealed
larvae; Occasionally
older sealed larvae.
Color of dead brood
Dull white, becoming
light brown, coffee
brown to dark brown
or almost black.
Dull white, becoming
yellowish white to
brown, dark brown, or
almost black.
Usually older sealed
larvae; Occasionally
young unsealed
larvae.
Grayish or straw
colored becoming
brown, grayish black,
or black. Head end
darker.
Consistency of dead brood
Soft, becoming sticky
to ropy.
Watery to pasty;
rarely sticky or ropy.
Odor of dead brood
Slight to pronounced
glue odor to glue-pot
odor.
Slightly to penetratingly
sour.
Character of scale
Uniformly lies flat on
lower side of cell. Adheres
tightly to cell wall. Fine,
threadlike tongue of dead
pupa adheres to roof of
cell. Head lies flat.
Usually twisted in cell.
Does not adhere
tightly to cell wall.
Rubbery.
Precautions in use of Drugs
Treating a colony with drugs does not destroy the disease causing organisms but rather prevents them from
multiplying. They also suppress outward manifestations
of the disease and disease can reappear after cessation
of chemical therapy. Therefore, USE DRUGS OR ANTIBIOTICS ONLY WHEN NECESSARY.
Watery & granular
tough skin forms a
sac.
None to slightly sour.
Head prominently
curled up. Does not
adhere tightly to cell
wall. Lies flat on
lower side of cell.
Rough texture.
Brittle.
Drugs should never be considered a substitute
for good beekeeping. The beekeeper should be able
to recognize the various diseases and treat colonies
accordingly. The beekeeper should in- spect every
colony at least two times a year (spring & fall) for
disease.
Use drugs only in the recommended dosage to avoid
poisoning of bees and brood. All drugs are toxic if used
in excessive quantities.
Any drug used may become mixed into honey. Do not
administer any drugs or antibiotics during a
honey flow or into honey supers. The only time to
feed medicinal agents is in the early spring during
colony buildup or in the fall after honey supers have
been removed.
MAAREC, the Mid-Atlantic Apiculture Research and Extension Consortium, is an official activity of five land grant universities and the U.S. Department of Agriculture. The following are operating members:
University of Delaware
Newark, Delaware
Rutgers University
New Brunswick, New Jersey
University of Maryland
College Park, Maryland
The Pennsylvania State University
University Park, Pennsylvania
West Virginia University
Morgantown, West Virginia
USDA/ARS
Bee Research Lab
Beltsville, Maryland
Requests for information or publications should be sent to: MAAREC, 501 ASI Building, University Park, PA 16802 Phone: (814)865-1896 Fax: (814)865-3048 Web site: http://MAAREC.cas.psu.edu
This publication is available in alternative media on request.
The mention of trade names or commercial products in this publication is for illustrative purposes only and does not constitute endorsement or recommendation by the Mid-Atlantic Apiculture Research and
Extension Consortium or their employees.
The U.S. Cooperative Extension Service and the U.S. Department of Agriculture provide Equal Opportunities in employment and programs.
*******
Participants in MAAREC also include state beekeeper associations, and State Departments of Agriculture from Delaware, Maryland, New Jersey, Pennsylvania and West Virginia.
MAAREC Publication 4.9
Visit the MAAREC Website at: http://MAAREC.cas.psu.edu